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Tesco said any customers who had already redeemed vouchers at three times the value "will not lose out" and should contact its customer service centre.

Tesco has about 16 million active Clubcard customers, according to figures released at its half-year results announcement.

Customers reacted with anger to the original changes, with one writing on Twitter: "We had £89 saved up in vouchers - worth £356. Now they are worth £267.

Tesco supermarket, Truro

"No advance warning, really really poor from @Tesco £tescoclubcard - been loyal Tesco customers for well over 10 years - because of clubcard. And what a load of BS about 'making it easier'."

Another wrote: "All clubcard boosts going to 3x. Everything we chose was 4x so this is a big reduction. But highlight was the inane corporate-speak lathered over the announcement...'this is not a reduction in boosts, oh no, this is TO MAKE IT EASIER FOR YOU TO UNDERSTAND' How dumb are we?"